1. Field of the Invention
The present invention relates to a manual control mechanism for a lift unit having a lift arm and a hydraulic cylinder for lifting the lift arm up and down. More particularly, the invention relates to a manual control mechanism of the above-noted type including a control valve configured as a three-position switchover valve for selectively providing lowering, neutral and elevating conditions according to a spool position for controlling movement of the hydraulic cylinder, a lift lever for manually operating the control valve and a operational path for guiding operational displacement of the lift lever.
2. Description of the Related Art
As known from the Japanese Patent Application “Kokai” No.: 2001-169607, as a mechanical control valve responsible for operation of a hydraulic cylinder of a lift unit mounted on e.g. a tractor, a position control valve is often employed. In a low-cost version of such construction, a control valve employed is usually of a simple manual operation type three-position switchover valve.
With such position control valve, the lift arm is lifted up and down according to an operation position of a position lever, so that e.g. a plowing depth for a rotary plowing operation can be easily set. On the other hand, with this valve, there occurs a certain amount of hysteresis in the course of the lifting operation, it is difficult to effect e.g. a grading operation which requires a fine lift adjustment on the order of a few millimeters.